Tuesday, February 17, 2009

3 or more dimensions

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This is a picture of my desktop. This is the normal compliment of applications I have loaded when I get on the air. Included are PowerSDR, DXlab's Commander, Keeper, View and Spot Collector, which amounts to a CAT control program, logbook, call look up and world map, and a DX cluster client. I love the tight integration of the DX lab suite. It's an amazing piece of software. In addition I have VE3NEA's CW skimmer loaded. CW skimmer is a program that works uniquely with the SDR and has the ability to decode CW stations in a 25khz piece of radio spectrum. It also has CAT control, so there is another slick little utility written by K5FR ddutil that allows several CAT control programs to be open at one time and each can address the radio. This program is like the swiss army knife of I/O connectivity between Ham radio software and Ham radio hardware.... Way Cool

CAT control is the protocol that was developed to allow computers to interact with legacy ham radio devices. Each manufacturer came up with his own proprietary set of commands. This is a closed source model and as such if someone wants to write an application to control a radio, he has to implament all these different flavors of command sets in order to serve the widest audience. It is partially what is wrong with the closed model. It destroys innovation by adding hours and hours of work to a products development. Flex uses the Kenwood command set which is perhaps the most robust of the protocols and very well supported across 3rd party applications. Usually only one program at a time can access the radio but through K5FR's slick little interface up to 5 programs can access one radio simultaneously. This is an example of the flexibility of the system at work. One day the capability does not exist and the next through some ham's ingenuity the capability does exist. Amazing. Who says we don't home brew anymore? Home brewing has just been kicked over to the software domain!!

In my case I have only 2 programs addressing the radio most of the time, sometimes I will also open up a contesting program (N1MM) as well.

Here is a closer snap of PowerSDR and Skimmer

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As I was heading off to bed last night I stopped into the shack, and was greeted with a monster pileup on 80CW. The DX was K5D (KP5) who is presently active on about every band and every mode. I had not worked him yet and decided to devote ten minutes to the endeavor. If I didn't get him in ten I was going to bed. I set up K5D in my RX VFO, but where to set up the TX vfo? As you can see the pileup is over 10khz wide with hundreds of stations calling. Just to walk through the pile to try and find where K5D was listening would take longer than the ten minutes I had allotted.

Now comes the concept of dimensionality. In a normal legacy radio like an Orion or a K-3, the signal comes into the antenna is filtered and mixed down to an IF. These radios have "roofing filters" which act like a sharp knife and cuts the bandwidth way down to as little as 200hz. This filtering is what gives this legacy type of radio its good IP3 and Dynamic range characteristics, but the cost is the loss of a ton of information that could be quite useful to the operator. That sliced signal is then sent further down the chain, demodulated and eventually ends up in your headphones. To change frequency you need to turn the knob. Every time you turn the knob and slice out a new spot to listen, you loose all the information you were just listening to. You say "well DUH that's how radio works!!!", but it doesn't have to be that way. You can have your cake AND eat it too, in fact you can have your cake and eat it THREE or maybe even FOUR. As you listen to your little slice of radio spectrum it is YOU who must do the work of deciding what you are listening to. You flip on the K-3 and tune to 3505 and you could either hear a signal or hear static. Since you've passed through a very narrow filtering scheme of lets say 200hz and a DSP filter of lets say 100Hz you don't know dick about what is 500hz away, and the only way you are going to know dick is to TURN THE KNOB and see if Dick is there. As soon as you turn the knob you now know what is happening on lets say 3505.5 but you no longer have a clue that K5D just came up on 3505, the freq from which you just tuned away.

This is the problem with a knob radio. It is very strongly one dimensional. You basically listen to one point in the radio spectrum and you are totally blind to anything else. The roofing filter basically guarantees that. It guarantees that you will have one slice and once slice alone to listen to. I once read a book by W9KNI the famous DXer and he described his routine, and it amounted to hours and hours of tuning up the band trying to identify every signal on the band. He started at the bottom and tuned to the top and then went to the bottom and started over. Most of his time therefore was spent listening to static. Enter the panadapter

The SDR works in a very different manner. A signal comes into the antenna and it is direct converted to audio. The most basic model in every ham's lexicon regarding direct conversion is the crystal radio. The AM signal hits the antenna is fed through a mixer (physically represented by the galena) and is directly demodulated to audio. If you have ever heard the output of a crystal radio through a good amplifier the quality of the audio is astounding. So the SDR inhales a wide spectrum of signal that is filtered passively and then demodulated through a mixer (like the crystal radio) to an audio baseband. The audio baseband is a few hundred khz wide. This is filtered and sent to quadrature detector which gives dimensionality to the signal. Every bit of analogue data that is fed into the quadrature detector comes out with a scalar value and a phase value. When you have that and a frequency you have the ability make a 2 dimensional VISUAL representation of what the RADIO is hearing. That allows your signals to now be displayed in your computer as a 2 dimensional slice of spectrum. You can now SEE the band!!!! You can see a whole big chunk of the band, up to 192khz of the band all at once, WITH YOUR EYES!!!! You now have both your ears AND your eyes involved in processing the data. Since you can see the static you never have to spend one minute listening to it. You just bypass it. With the SDR's point and click kind of control interface you can merely click on the signal leaving the static behind. W9KNI would spend a whole lot less of his time listening to static, AND he could see that a station came on the air below the point he just passed in his search and destroy mission.

What you see in the panadapter is what the radio hears. What you hear is a little slice of that wide spectrum, the slice you choose to hear. Its that little slice that you choose to demodulate as AM or FM or SSB or digital or CW. It is the little slice that you choose to filter to 8khz or 200 hz or as little as 11hz. But you need to understand you are no longer blind!!! You can hear and you can see. In the land of the blind (legacy radio design) you are King because you can see!!!

Here is what you see:

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This is an extract from the K5D pileup. The signal under the green line is K5D. The green line represents the bandwidth of a 100hz filter window, centered 350hz above the center frequency (the red line). The yellow line is my mouse cursor and will become where my transmit VFO frequency will be located once I click it. I know the entire extent of the pileup at a glance. If K5D is working someone, the pileup goes pretty quiet (except for the few dorks who just sit there and transmit no matter what). Usually what you will SEE is the interaction between k5D and the station he is working. It looks like a dance. K5D's signal turns on and then stops. A few hundred milliseconds later the station he is working shows up on the pandadapter and then stops. Then K5D comes back on the screen. You can follow the dance as well in your headphones. K5D dances on the screen and sings in your ears, then the station being worked then back to K5D. The SDR has a watch receiver and you can turn that on and see and hear both sides of the dance, one station in the left ear and one station on the right, or you can pan those stations anywhere across the stereo field.

The SDR has the ability to drop the transmitter exactly onto the frequency of the station who is being worked by K5D with the click of a mouse button. There is no need to be spinning vfo knobs trying to zero in on the tail end. You can now see exactly where you want to transmit and "click" you are transmitting exactly where you want.

Enter the third dimension. In a pile of this magnitude with several hundred stations calling, finding the tail end freq is not always easy even with the ability to see, because at any one time there my still be 30 or 40 stations calling. Enter CW skimmer, the third dimension. Skimmer processes all that 25 khz of bandwidth and spits out call signs, and it has a little yellow or red circle next to the processed callsign. It processes continuously and keeps making changes until it is sure of what it is copying. It also looks for common phrasing like CQ QRL and 599 (or 5NN which it understands as 599). Skimmer also watches the dance and when it hears 599 it lists that next to the callsign of the station that sent it and turns the circle connected to his call red. So all I have to do is watch the screen and skimmer tells me where the station is that is in QSO with K5D

Here is the shot of skimmer

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If you look closely you can see the 599. Now its a simple matter

Click on split, center K5D in the audio passband where you like him, hit <> in PowerSDR which switches the contents of each VFO to the other, hit the little red circle next to the 599 station, and hit <> again.

What just happened is I entered the tail end frequency into my transmit VFO using CAT commands from Skimmer, and in 3 clicks I am ready to tail end in a pileup of 100's of stations. This is the third dimension, the dimension of intelligence. Skimmer assigns the blips on the panadapter names that mean something to me, and therefore I can use that data to make rapid and correct decisions.

The end of my K5D saga? I got a new one, FIRST CALL. I was headed to bed with a new one in the log in well under ten minutes.

The future? My F5K has 2 independent receivers. Imagine 2 receivers on 2 bands with 2 instances of skimmer. Imagine that skimmer/RX1 is set to K5D on 80M and skimmer/RX 2 is set to the K5D pileup on 160M. SInce the F5K is triplex and not half duplex like most legacy radios, its a simple matter to work K5D on 80M and then in one click be ready to work him on 160 (I have seperate amp and antenna chains on each ot those bands so its a one click proposition for the way I have things set up) That's almost living in the 4th dimension. A dimension where I have single signal audio, panadapter visual, a modicum of intelligence and multiple processes on different bands all going on at once, all at my finger tips, eyeballs and eardrums.

In fact I didn't head off to bed immediately. If you look back to the first screen you will see that K5D is also spotted on 30M. I decided to put them in log on that band also. I clicked on the spot and Spot Collector (thanks to DDUTIL) switched my rig to 30M and switched skimmer to 30M as well. On 30, the pileup was no where near as severe, but the pileup stations were very very weak, K5D was very strong. Skimmer and the F5K is a very sensitive combo and I was still able to determine the correct tail end freq by "watching" stations that were virtually under the noise. The result, worked him in 2 calls. This thing is a DX howitzer.

One last thing. People crow and crow about roofing filters. All I hear about is roofing filters. WHAT I JUST DID COULD NOT BE DONE IN A RADIO WITH A ROOFING FILTER!! To do it you need to take advantage of SDR architecture. Also note: I did not NEED a roofing filter. My radio was subjected to hundreds of strong signals, and my reception of K5D in both in instances was single signal with absolutely no intermod and no blocking issues. That is the nature of a direct conversion radio. It's a naturally strong design without all the band aids. Think about that. What would a roofing filter have bought me in this application? The answer is much reduced functionality. Much reduced efficiency. Stick that in your roofing filtered legacy radio's hookah and smoke it. (with due respect to Mike Phelps)

Call to arms

Hear Ye Hear Ye

If you're interested in writing something interesting for this blog regarding your SDR experience let me know. I would like to include things like how your SDR contest station is set up, or your VHF station that uses SDR as the system center, feats of weak signal work or how well the SDR works in various challenging situations. If you are a foreign ham and would like to comment on the growth of SDR in your particular part of the world. Bring it on!

I reserve the right to publish or not, but I'm pretty open to documenting a wide variety of honest experiences from users, for readers to explore. The understanding of SDR in our hobby is so nascent, that I want the reader to be able to see the value of SDR through the eyes of YOUR experience and enthusiasm.